Ferritic creep-resisting steels



United States Patent FERRITIC CREEP-RESISTIN G STEELS Henry William Kirkby and Charles Sykes, Sheilielti, England, assignors to Thos. Firth & John firown Limited, Shefiield, England, a British company N 0 Drawing. Application April 1, 1953, Serial No. 346,255

Claims. (Cl. 75-426) This invention comprises improvements relating to ferritic creep-resisting steels.

It is well known that the majority of creep-resisting steels (ferritic and austenitic) contain molybdenum and this element is generally regarded as an essential constituent in such materials. In ferritic creep-resisting steels, molybdenum is invariably present, e. g. carbon-molybdenum, chromium-molybdenum, molybdenum-vanadium, chromium-molybdenum-vanadium, and other special steels.

Molybdenum is known to be an alloying element of strategic importance and hitherto has been regarded as a metal vital to a countrys economy in so far as alloy steels suitable for high temperature applications are concerned.

The present invention provides alloy compositions which, without entailing the use of molybdenum as an alloying constituent, have creep-resisting properties comparable with or superior to those of the known molybdenum-containing creep-resisting steels referred to above.

The alloys provided by the invention comprise the following range of composition:

Carbon 0.02 to 0.15%. Silicon 0.05 to 1.0%. Manganese 0.05 to 2.0%. Chromium 0.10 to 3.5%. Vanadium 0.05 to 1.0%. Titanium 0.05 to 0.40%. Boron 0.003 to 0.05%. Iron The substantial remainder.

Carbo 0.06 to 0.12%. Silicon 0.10 to 0.50%. Manganese 0.50 to 1.0%. Chromium 0.40 to 2.0%. Vanad 0.25 to 0.75%. Titanium 0.075 to 0.30%

ICC

The following stress rupture properties have been obtained on selected compositions within the range of the invention:

Hgurs to Fig.0- 0 Si, Mn, Ni Gr, v Ti, B i at Alloy peiperperper'- perpeiperpeiig g ggg" cent cent cent cent cent cent cont cent 16011 at 0.65 0.74 0.05 0.64 0.43 0.08 0.005 163. 0.35 1.02 nil 0.88 0.74 0.20 0.005 116%. 0.31 0.94 nil 0.64 0.51 0.24 0.01 300Unbroken. 0.31 0.76 nil 0.75 0. 51 0.22 0.005 389. 0.35 0.96 0.07 3.19 1.0 0.14 0.005 306Unbroken.

On alloy A, a creep test under conditions 6 tons/sq. inch at 650 C. gave a creep deformation of 0.125% in 300 hours. This compares very favourably with the creep properties of known molybdenum-vanadium creepresisting steels.

We claim:

1. A creep resistant ferritic alloy steel comprising carbon 0.02 to 0.15%, silicon 0.05 to 1.0%, manganese 0.05 to 2.0%, chromium 0.10 to 3.5%, vanadium 0.05 to 1.0%, titanium 0.05 to 0.40%, boron 0.003 to 0.05%, and the balance iron with impurities in ordinary amounts.

2. A creep resistant ferritic alloy steel comprising carbon 0.02 to 0.15 silicon 0.05 to 1.0%, manganese 0.05 to 2.0%, chromium 0.10 to 3.5%, vanadium 0.05 to 1.0%, titanium 0.05 to 0.40, boron 0.003 to 0.05%, nickel 0 to 1% and the balance iron with impurities in ordinary amounts.

3. A creep resistant ferritic alloy steel comprising carbon 0.06 to 0.12%, silicon 0.10 to 0.50%, manganese 0.50 to 1.0%, chromium 0.40 to 2.0%, vanadium 0.25 to 0.75%, titanium 0.075 to 0.30%, boron 0.003 to 0.01%, and the balance iron with impurities in ordinary amounts.

4. A creep resistant ferritic alloy steel comprising carbon 0.02 to 0.15%, silicon 0.05 to 1.0%, manganese 0.05 to 2.0%, chromium 0.10 to 3.5%, vanadium 0.05 to 1.0%, titanium 0.05 to 0.40%, boron 0.003 to 0.05%, and the balance iron with impurities in ordinary amounts, characterised by the total absence of molybdenum from the constituents.

5. A creep resistant ferritic alloy steel comprising carbon 0.02 to 0.15 silicon 0.05 to 1.0%, manganese 0.05 to 2.0%, chromium 0.10 to 3.5%, vanadium 0.05 to 1.0%, titanium 0.05 to 0.40%, boron 0.003 to 0.05%, and the balance iron with impurities in ordinary amounts, characterised by the total absence of both molybdenum and tungsten from the constituents.

References Cited in the file of this patent UNITED STATES PATENTS 2,480,151 Malcolm Aug. 30, 1949 2,542,220 Urban et al. Feb. 20, 1951 2,572,191 Payson Oct. 23, 1951 

1. A CREEP RESISTANT FERRITIC ALLOY STEEL COMPRISING CARBON 0.02 TO 0.15%, SILICON 0.05 TO 1.0%, MANGANESE 0.05 TO 2.0%, CHROMIUM 0.10 TO 3.5%, VANADIUM 0.05 TO 1.0%, TITANIUM 0.0K TO 0.40%, BORON 0.003 TO 0.05% AND THE BALANCE IRON WITH IMPURITIES IN ORDINARY AMOUNTS. 